Spindle motor and bearing assembly

ABSTRACT

The fixed shaft type spindle motor of the invention has a fixed shaft extending from a base and a rotor hub rotatably supported thereon through a bearing. Where the bearing is a compound ball bearing, a larger diameter portion of a stepped connection member is fixed within the upper end of the outer ring of the compound ball bearing and a smaller diameter portion of the connection member is fixed to the rotor hub. The rotary shaft type spindle motor has a rotary shaft extending within the rotor hub, and the rotary shaft is rotatably supported through the bearing, with the larger diameter portion of the connection member fixed within the lower end of the outer ring of the compound ball bearing and the smaller diameter portion of the connection member fixed to the base.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a spindle motor and a bearing assemblyfor use in office automation equipment such as a computer and peripheralequipment thereof as a driving device/component for the rotatingmechanism thereof, specifically to the spindle motor and the bearingassembly to enhance the run-out accuracy/nonrepeatable runout (NRRO) ofa motor, and reliability, low noise, acoustic life, and rigidity, etc.

2. Description of the Prior Art

Spindle motors for driving a magnetic disk, e.g., a hard disk drive as aperipheral device of a computer, are classified broadly into two typesin terms of the structure: the fixed shaft type in which a fixed shaftis installed upright on a base, and a rotor hub is supported to freelyrotate on the fixed shaft through a bearing interposed between the fixedshaft and the rotor hub; and the rotary shaft type in which a rotaryshaft is vertically installed on a rotor hub, and the rotary shaft issupported to freely rotate on a base through a bearing interposedbetween the rotary shaft and the base.

Generally, the fixed shaft type is provided with, as shown in FIG. 9, abase (flange) 02, a fixed shaft 010 that is installed upright on thebase 02, a rotor hub (hub member) 03 that rotates relative to the base02, and a bearing means 04 interposed between the fixed shaft 010 andthe rotor hub 03. A recording medium such as a magnetic disk (not shown)is mounted on the rotor hub 03. A stator 015 is installed on the outerperipheral surface of an inner cylindrical wall 014 of the base 02, anda permanent magnet 016 is installed on the inner peripheral surface ofan outer circumferential wall 013 of the rotor hub 03 so as to face theouter peripheral surface of the stator 015. A feeder 017 feeds currentto the windings of the stator 015 and is connected to a flexible printedcircuit board 037.

The bearing means 04 is a compound ball bearing, and an inner ring 06thereof is fixed to the outer surface of the fixed shaft 010, and anouter ring 05 thereof is fixed to the inner peripheral surface of aninner circumferential wall 032 of the rotor hub 03. A part of the innerring 06 can be formed integrally with the fixed shaft 010 according tocircumstances, as shown in FIG. 9; and the outer ring 05 can be formedintegrally with the whole structure of the compound ball bearing incertain cases, as shown in the same figure.

The rotary shaft type is also provided with, as shown in FIG. 10, thebase (flange) 02, the rotor hub (hub member) 03 that rotates relative tothe base, a rotary shaft 020 that is vertically installed on the rotorhub 03, and the bearing means 04 interposed between the rotary shaft 020and the base 02. The recording medium such as a magnetic disk (notshown) is mounted on the rotor hub 03. The stator 015 is installed onthe outer peripheral surface of the inner cylindrical wall 014 of thebase 02, and the permanent magnet 016 is installed on the innerperipheral surface of the outer circumferential wall 013 of the rotorhub 03 so as to face the outer peripheral surface of the stator 015. Thesymbol 017 denotes the feeder for feeding current to the windings of thestator 015, which is connected to a flexible printed circuit board 037.

The bearing means 04 is a compound ball bearing, and the inner ring 06thereof is fixed to the outside to the rotary shaft 020, and the outerring 05 thereof is fixed to the inner peripheral surface of thecylindrical wall 014 of the base 02. A part of the inner ring 06 can beformed integrally with the rotary shaft 020 according to circumstances,as shown in FIG. 10; and the outer ring 05 can be formed integral withthe whole structure of the compound ball bearing in certain cases, asshown in the same figure.

In a certain case, the rotor hub 03 and the rotary shaft 020 eachmanufactured separately can be assembled into a unit, as shown in FIG.10; and in another case, they can be manufactured as an integral unitfrom the beginning. In the latter case, a part of the inner ring 06cannot be formed integrally with the rotary shaft 020.

In any type of the spindle motor 01, the rotor hub 03 thereof issupported on the base 02 to freely rotate through the compound ballbearing 04 as a rolling bearing interposed between the base 02 and therotor hub 03. And, the inner ring 06 of the compound ball bearing 04 isfixed to the outside of the fixed shaft 010 vertically installed on thebase 02 or to the rotary shaft 020 vertically installed on the rotor hub03. The outer ring 05 thereof is fixed to the inner peripheral surfaceof the inner circumferential wall 032 of the rotor hub 03 or to theinner peripheral surface of the inner cylindrical wall 014 of the base02.

Now, recent demands of the hard disk drive show a remarkable tendencytoward increase in the recording capacity, to enhance the impactresistance, to lower the noises, to increase the data access speed, andso forth. In order to answer these requirements, the roller bearing of aspindle motor has gone through improvements in the material composition,enhancements of the precision of the inner and outer rings and rollingelements, etc.

However, when the inner and outer rings and the balls (rolling elements)are made of steel such as bearing steel, metal-to-metal contact occursbetween the rolling surfaces of the inner and outer rings and thesurfaces of the balls, which contact effects galling and wear todeteriorate the acoustic characteristic, leading to a problem in theacoustic life (recently, the life of the spindle motor is evaluated notby the fatigue life, but by the acoustic life). Further, frettingcorrosions (impressions, dilapidated surfaces) form on the rollingsurfaces due to shocks and vibrations during transportation, which alsodeteriorates the acoustic life and the precision of rotation.

Especially in recent years, the rotational speed of a spindle motor isincreased to higher than 7200 rpm, and the sound of rotation of themotor becomes increased to that degree, which tends to shorten theacoustic life. Also, in the future, a need for still further increase ofthe recording capacity is estimated in view of the demand for recordingvideo images and so forth. In order to answer such demands and estimatedfuture problems, the foregoing improvements in the material compositionand enhancements of the working precision and the like will not besufficient.

In recent years, ball materials have been tested and examined whichexceed in the non-agglutination property and in wear resistance, andnitride silicon ceramics have been adopted as the rolling elementmaterial. There have been discussions about the limitation of therolling bearing itself, including the ceramic ball bearing made of suchnew materials, and employment of a fluid bearing has been suggested as asolution to these problems.

FIG. 11 illustrates a rotary shaft type spindle motor 01 with such afluid bearing. This spindle motor 01 is provided with a base (flange)02, a rotor hub (hub member) 03 that rotates relative to the base 02, arotary shaft 020 that is vertically installed on the rotor hub 03, and afluid bearing 030 interposed between the rotary shaft 020 and the base02.

A sleeve 031 of the fluid bearing 030 sheathes the rotary shaft 020, andis fixed to the inner peripheral surface of the inner cylindrical wall014 of the base 02. Lubricating oil is supplied into the sliding areabetween the sleeve 031 and the rotary shaft 020, and herringbones(<-shaped grooves) 033 formed on the circumferential surface of therotary shaft 020 raise the pressure of the lubricating oil, with therotation of the rotary shaft 020, which floats the rotary shaft 020 upin the sleeve 031.

Although not detailed in the drawing, similar herringbones are formed onan edge surface of a thrust ring 034 fixed to a lower part of the rotaryshaft 020, and lubricating oil is supplied into a gap between the edgesurface and an inner surface of a counter plate 037 fixed to the lowerend of the sleeve 031. As the rotary shaft 020 turns, the herringbonesraise the pressure of the lubricating oil, which makes the counter plate037 receive the thrust that acts on the rotary shaft 020.

Therefore, the base 02 supports the rotary shaft 020 of the rotor hub 03for free rotation through the fluid bearing 030 interposed therebetween.The other structure of the motor is basically identical to the spindlemotor having the compound ball bearing.

On the other hand, in the fixed shaft type spindle motor with a fluidbearing, which is not illustrated, the sleeve 031 of the fluid bearing030 is fit to an inner peripheral surface of a wall formed on the rotorhub 03, and a fixed shaft is installed upright on the base 02 andsheathed with the sleeve 031. Therefore, the fixed shaft supports therotor hub 03 to allow free rotation through the fluid bearing 030interposed therebetween.

Regardless of whether a ball bearing or a fluid bearing is used, andregardless of whether the spindle motor is a fixed shaft type or arotary shaft type, the installation of the bearing in the spindle motoris carried out by one of the following methods: press-fitting to thecounterpart (rotating components and fixed components), adhesion byadhesives, and press-fit adhesion using both of these.

In case of the press fitting method, the precision of the shape(circularity, cylindricality, surface roughness) of the inner or outerperipheral surface of the counterpart influences the shape from theouter peripheral surface of the outer ring and the inner peripheralsurface of the inner ring of the rolling bearing which influence istransferred to the rolling surfaces of the inner and outer rings, i.e.,deformation of the rolling surfaces of the inner and outer rings. Also,the external stress caused by press fitting propagates through the outerperipheral surface of the outer ring or through the inner peripheralsurface of the inner ring, and produces permanent deformations on therolling surfaces of the inner and outer rings through the rollingelements to form impressions thereon, which reduces the reliability ofthe run-out accuracy/NRRO, and the acoustic life, etc., of the motor. Inthe fluid bearing, the clearance between the sleeve and the shaftvaries, which varies the rigidity.

In using an adhesive, stress is produced when the adhesive hardens,which deforms the bearing, also damaging the reliability of the run-outaccuracy, increasing noise, and reducing the acoustic life of the motor,and so forth. Further, in the rotary shaft type spindle motor, theassembly of the stator 015 on the outer peripheral surface of thecylindrical wall 014 of the base 02 reduces the accuracy of the innerdiameter of the cylindrical wall 014, which, in turn, reduces thebearing precision.

Further, in case of the foregoing press-fitting, adhesion, and press-fitadhesion methods for mounting the bearing, an adhesion groove (refer toadhesion groove 040 in FIG. 9, adhesion groove 041 in FIG. 10) forintroducing the adhesive and a run-off groove are needed on the bearingmounting surface on the side of the counterpart, which requireadditional time (man-hours), leading to a cost increase.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing problems,and it is an object of the invention to provide a spindle motor and abearing assembly that resolve the foregoing problems of the conventionalspindle motor, and that remove adverse influences of stress on theprecision of the rolling surfaces of the inner and outer rings throughthe outer peripheral surface of the outer ring and the inner peripheralsurface of the inner ring of the bearing. In other words, the object isto reduce the effect of stress on shape precision (circularity,cylindricality, surface roughness) of the inner or outer peripheralsurface of the counterpart, which stress is created in mounting thebearing by press-fitting, adhesion, or press-fit adhesion, and tothereby enhance the reliability of the run-out accuracy/NRRO, reduce thenoise, and prolong the acoustic life, etc., of the spindle motor, and toreduce the manufacturing cost thereof.

According to the first aspect of the invention, the spindle motor is afixed shaft type spindle motor in which a fixed shaft is verticallysupported on a base and a rotor hub is supported for free rotation bythe fixed shaft through a bearing which is a compound ball bearing, witha larger diameter portion of a connection member fixed within an end ofan outer ring of the compound ball bearing, and a smaller diameterportion of the connection member fastened to the rotor hub. Thus, theouter ring of the compound ball bearing is fastened to the rotor hubthrough the connection member.

As a result, the rotor hub (the component on the rotating side) beingone of the two counterparts (a component on the rotating side and acomponent on the fixing side) that have the compound ball bearingmounted therebetween can omit the inner peripheral wall which hasconventionally been regarded as necessary for fitting the outer ring ofthe compound ball bearing thereto. Therefore, the stress otherwiseresulting from the shape precision (circularity, cylindricality, surfaceroughness) of the inner peripheral surface of the wall, and the stresscaused by the press-fitting, adhesion, or press-fit adhesion mounting ofthe bearing are eliminated. Accordingly, adverse influences on theprecision of the rolling surfaces of the inner and outer rings throughthe outer peripheral surface of the outer ring of the bearing areeliminated, thereby enhancing the reliability of the run-outaccuracy/NRRO, the noises, and the acoustic life, etc., of the spindlemotor.

Further, since the rotor hub can be configured without the innerperipheral wall, which has conventionally been regarded as necessary forfitting the outer ring of the compound ball bearing thereto, theadhesion groove (the groove for filling adhesives) and the run-offgroove that are conventionally formed on the inner peripheral surface ofthe wall become unnecessary, thereby reducing the man-hours andmanufacturing cost.

According to the second aspect of the invention, the compound ballbearing is substituted with a fluid bearing, with the larger diameterportion of the connection member fixed within an end of a sleeve of thefluid bearing, and the smaller diameter portion of the connection memberfastened to the rotor hub. Thus, the sleeve of the fluid bearing isfastened to the rotor hub through the connection member.

Also with use of a fluid bearing, the inner peripheral wall, which hasconventionally been regarded as necessary for fitting the sleeve of thefluid bearing thereto, may be eliminated, along with the aforementionedstresses. Accordingly, adverse influences on the precision of thesliding surfaces of the sleeve and the fixed shaft and on the clearancetherebetween are eliminated, thereby enhancing the reliability of therun-out accuracy/NRRO, the noises, the acoustic life, and the rigidity,etc., of the spindle motor.

Further, since the inner peripheral wall, which has conventionally beenregarded as necessary for fitting the sleeve of the fluid bearingthereto, is omitted, the adhesion groove and the run-off groove that areconventionally formed on the inner peripheral surface of the wall becomeunnecessary, thereby reducing the man-hours and the manufacturing cost.

According to a third aspect of the invention, there is provided a rotaryshaft type spindle motor in which a rotary shaft is fixed to a rotor huband the rotary shaft is supported for freely rotating through a bearing,wherein the bearing is a compound ball bearing. A larger diameterportion of a stepped connection member is fixed within an end of anouter ring of the compound ball bearing, and a smaller diameter portionof the connection member is fixed to the base. Thus, the outer ring ofthe compound ball bearing is fastened to the base through the connectionmember.

As a result, the base (the component on the fixed side) being the one ofthe two counterparts (the component on the rotating side and thecomponent on the fixed side) that mount the compound ball bearingtherebetween can be made without the inner peripheral wall, which hasconventionally been regarded as necessary to fit the outer ring of thecompound ball bearing thereto. Therefore, the stress resulting from theshape precision (circularity, cylindricality, surface roughness) of theinner peripheral surface of the wall and the stress caused by thepress-fitting, adhesion, or press-fit adhesion method of mounting thebearing are eliminated. Accordingly, adverse influences on the precisionof the rolling surfaces of the inner and outer rings through the outerperipheral surface of the outer ring of the bearing are eliminated,thereby enhancing the reliability of the run-out accuracy/NRRO, thenoises, and the acoustic life, etc., of the spindle motor.

Further, since the inner peripheral wall, which has conventionally beenregarded as necessary for fitting the outer ring of the compound ballbearing thereto, is eliminated, the adhesion groove and the run-offgroove that are conventionally formed on the inner peripheral surface ofthe wall become unnecessary, thereby reducing the man-hours and themanufacturing cost.

In a fourth aspect of the invention, the compound ball bearing of thethird aspect is replaced with a fluid bearing, with a larger diameterportion of the stepped connection member fixed within an end of a sleeveof the fluid bearing, and the smaller diameter portion of the connectionmember fastened to the base. Thus, the sleeve of the fluid bearing isfastened to the base through the connection member.

As a result, in the fourth aspect also, the aforementioned stresses areeliminated and, accordingly, adverse influences on the precision of thesliding surfaces of the sleeve and the fixed shaft and on the clearancebetween the sliding surfaces of the two are eliminated, therebyenhancing the reliability of the run-out accuracy/NRRO, the noise, theacoustic life, and the rigidity, etc., of the spindle motor.

Further, in the fourth aspect also, because the inner peripheral wall,which has conventionally been regarded as necessary for fitting thesleeve of the fluid bearing thereto, is eliminated, the adhesion grooveand the run-off groove can also be eliminated, thereby reducing theman-hours and lowering the manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 1 is a sectional view of a fixed shaft type spindle motor accordingto the first embodiment of the invention;

FIG. 2 is an exploded view of the spindle of FIG. 1;

FIG. 3 is a sectional view of a rotary shaft type spindle motoraccording to a second embodiment of the invention;

FIG. 4 is an exploded view of the spindle motor of FIG. 3;

FIG. 5 is a sectional view of a fixed shaft type spindle motor accordingto a third embodiment of the invention;

FIG. 6 is an exploded view of the spindle motor of FIG. 5;

FIG. 7 is a sectional view of a rotary shaft type spindle motoraccording to a fourth embodiment of the invention;

FIG. 8 is an exploded view of the spindle motor of FIG. 7;

FIG. 9 is a sectional view of a conventional fixed shaft type spindlemotor using a compound ball bearing;

FIG. 10 is a sectional view of a conventional rotary shaft type spindlemotor using a compound ball bearing; and

FIG. 11 is a sectional view of a conventional rotary shaft type spindlemotor using a fluid bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the invention will be described with referenceto FIG. 1 and FIG. 2.

As shown in FIG. 1 and FIG. 2, the fixed shaft type spindle motor 1 ofthe first embodiment has a fixed shaft 10 installed upright (verticallyupward) on a flange base 2, in which the fixed shaft 10 is fixed withina central circular hole 11 in the flange base 2. An inner ring 6 of anupper half portion of a compound ball bearing 4 is fixed to the upperreduced diameter portion of the fixed shaft 10. The inner ring portion(6) of the lower half of the compound ball bearing 4 is formedintegrally with the fixed shaft 10.

An outer ring 5 of the compound ball bearing 4 is an integral structurewhich extends over the whole length of the compound ball bearing 4. Onthe upper end of the outer ring 5 is formed a step portion having anenlarged inner diameter. A larger diameter portion 8 a of a steppedconnection member 8 (also having a smaller diameter portion 8 b) isfixed within the step formed in the upper end of the outer ring 5. Thesmaller diameter portion 8 b of the connection member 8 is fixed withinga central circular hole 9 of a rotor hub 3.

Therefore, since the rotor hub 3, connection member 8, and the outerring 5 of the compound ball bearing 4 are coupled together into a singleunit, the rotor hub 3 is supported for free rotation by the fixed shaft10 through the connection member 8 and the compound ball bearing 4.Because the outer ring 5 of the compound ball bearing 4 is fixed to therotor hub 3 through the connection member 8, an inner peripheral wall(refer to the inner peripheral surface of the inner circumferential wall032 of the rotor hub 03 in FIG. 9), which has conventionally beenregarded as necessary to secure the outer ring 5 of the compound ballbearing 4 to the rotor hub 3, becomes unnecessary and is omitted.

A magnetic disk (not shown) is mounted on a mounting surface 12 of therotor hub 3. The other rotating bodies requiring a high run-outaccuracy/NRRO and/or low noise can be mounted thereon.

Plural balls (rolling elements) 7 are accommodated between the outerring 5 and the inner ring 6, which are arrayed around the circumferencein a vertical two-stage configuration. The balls 7 travel on concaverolling surfaces that are formed facing each other on the innerperipheral surface of the outer ring 5 and on the outer peripheralsurface of the inner ring 6.

A stator 15 is fitted around the outer peripheral surface of an innercylindrical wall 14 of the base 2, and a permanent magnet 16 is mountedaround the circumference on the inner peripheral surface of an outercircumferential wall 13 of a larger diameter portion of the rotor hub 3,facing the outer peripheral surface of the stator 15. A feeder 17connects the windings of the stator 15 to a flexible printed circuitboard 37. The symbol 18 denotes a plaque.

In the first embodiment, the fixed shaft 10, the compound ball bearing4, and the connection member 8 are integrally assembled in advance as aunit, as shown in FIG. 2. With the bearing assembly thus assembled, theprojecting end of the fixed shaft 10 is fixed within the centralcircular hole 11 of the base 2, and the smaller diameter portion 8 b ofthe connection member 8 is fixed withing the central circular hole 9 ofthe rotor hub 3, whereby the fixed shaft type spindle motor 1 of thefirst embodiment is completed.

When power is supplied from the feeder 17 connected to the flexibleprinted circuit board 37 to the windings of the stator 15, according tothe operating principle of the synchronous motor, the rotor hub 3 withthe permanent magnet 16 starts to rotate as one body with the connectionmember 8 and the outer ring 5. That is, the rotor hub 3 is borne by thecompound ball bearing 4 through the connection member 8 to rotate aboutthe fixed shaft 10.

The rotor hub 3 is one of the two counterparts, the rotor hub 3 beingthe component on the rotating side and the base 2 being the component onthe fixed side. Because the compound ball bearing 4 eliminates need forthe inner wall, which has conventionally been regarded as necessary forfitting the outer ring 5 of the compound ball bearing 4 to the rotor hub3, the stress resulting from faults in the shape precision (circularity,cylindricality, surface roughness) of the inner peripheral surface ofthe wall, and the stress caused by the mounting of the bearing areeliminated. Accordingly adverse influences on the precision of therolling surfaces of the inner and outer rings 6, 5 through the outerperipheral surface of the outer ring 5 of the compound ball bearing 4are eliminated, so that the reliability of the run-out accuracy/NRRO,the noises, and the acoustic life, etc., of the spindle motor 1 can beenhanced.

Further, because the rotor hub 3 is one of the two counterpartsconnected through the compound ball bearing 4 omits the inner wall whichhas conventionally been regarded as necessary for fitting the outer ring5 of the compound ball bearing 4 to the rotor hub 3, the adhesion groovefor introducing adhesive and the run-off groove that are conventionallyformed on the inner peripheral surface of the wall become unnecessary,which reduces man-hours and lowers the manufacturing cost.

Further, since the compound ball bearing 4, the fixed shaft 10, and theconnection member 8 are assembled in advance into one unit, fasteningthe fixed shaft 10 to the base 2 and fastening the smaller diameterportion 8 b of the connection member 8 to the rotor hub 3 will serve toassemble the compound ball bearing 4 between these two counterparts,thus the work of mounting the compound ball bearing 4 becomes extremelyeasy to perform.

Since the inner ring portion (6), which is on the lower half of the twounit ball bearing portions constituting the compound ball bearing 4, isformed integrally with the fixed shaft 10, assembling the compound ballbearing 4, the fixed shaft 10, and the connection member 8 in advanceinto one assembly unit will produce a still greater advantage. If thesecomponents were not assembled in advance, mounting the compound ballbearing 4 on the fixed shaft 10 with the inner ring portion (6)integrally formed thereon would lead to a troublesome procedureinvolving insertion of the balls (rolling elements) 7 between the outerring 5 and the fixed shaft 10. Consequently, the mounting of thecompound ball bearing 4 would become still more complicated anddifficult.

Next, a second embodiment of the invention will be described withreference to FIG. 3 and FIG. 4 wherein the parts corresponding to thoseof the fixed shaft type spindle motor in the first embodiment are giventhe same symbols.

As shown in FIG. 3 and FIG. 4, the rotary shaft type spindle motor 1 ofthe second embodiment has a rotary shaft 20 installed in the rotor hub3, in which the rotary shaft 20 is fixed withing the central circularhole 9 of the rotor hub 3. The inner ring 6 of the lower half of thecompound ball bearing 4 is fixed to the lower reduced diameter portionof the rotary shaft 20 in FIG. 3. The inner ring portion (6) of theupper half of the compound ball bearing 4 is formed integrally with therotary shaft 20.

The outer ring 5 of the compound ball bearing 4 is formed as a nintegral structure which extends the whole length of the compound ballbearing 4. On the lower end of the outer ring 5 is formed a step made byenlarging the inner diameter thereof. The larger diameter portion 8 a ofthe stepped connection member 8 is fixed within the step formed on thelower end of the outer ring 5. The smaller diameter portion 8 b of theconnection member 8 is fixed within the central circular hole 11 of theflange base 2. Further, the larger diameter portion 8 a is seated on aninner surface surrounding the central circular hole 11 of the base 2;however it is not necessarily seated in this manner.

Therefore, since the base 2, connection member 8, and the outer ring 5of the compound ball bearing 4 are coupled into one unit, the base 2supports the rotary shaft 20 of the rotor hub 3 for free rotationthrough the connection member 8 and the compound ball bearing 4. Sincethe outer ring 5 of the compound ball bearing 4 is fixed to the base 2through the connection member 8, the inner peripheral wall (refer to theinner cylindrical wall 014 of the base 02 in FIG. 10), which hasconventionally been regarded as necessary for fitting the outer ring 5of the compound ball bearing 4 to the base 2, becomes unnecessary.Therefore, the base 2 is not provided with such an inner peripheralwall. The base 2 has the inner cylindrical wall 14 formed uprightthereon with an inner peripheral surface facing the outer peripheralsurface of the outer ring 5. However, the outer ring 5 is not fixed tothis inner peripheral surface of the inner cylindrical wall 14.

In the second embodiment, the rotary shaft 20, the compound ball bearing4, and the connection member 8 are integrally assembled in advance as aunit, as shown in FIG. 4. With the bearing thus assembled, theprojecting end of the rotary shaft 20 thereof is fixed within thecentral circular hole 9 of the rotor hub 3, and the smaller diameterportion 8 b of the connection member 8 is fixed within the centralcircular hole 11 of the base 2, whereby the rotary shaft type spindlemotor 1 of the second embodiment is assembled.

The second embodiment is different from the first embodiment in theforegoing particulars, however it is not different in the other internalstructure of the compound ball bearing 4, the structure of the motor,and so forth; and the detailed description will be omitted.

With the second embodiment as described above, when the power issupplied from the feeder 17 to the windings of the stator 15, the rotorhub 3 with the permanent magnet 16 starts to rotate as one body with therotary shaft 20 and the inner ring 6. The base 2 supports the rotaryshaft 20 of the rotor hub 3 for free rotation through the connectionmember 8 and the compound ball bearing 4.

The second embodiment also can be made without the inner peripheral wallwhich has conventionally been regarded as necessary for fitting theouter ring 5 of the compound ball bearing 4 to the base 2. As a result,the stress resulting from the shape precision (circularity,cylindricality, surface roughness) of the inner peripheral surface ofthe wall, and the stress caused by the press-fitting, adhesion, orpress-fit adhesion as the method of mounting the bearing are eliminated.Accordingly adverse influences on the precision of the rolling surfacesof the inner and outer rings 6, 5 through the outer peripheral surfaceof the outer ring 5 of the compound ball bearing 4 are eliminated, sothat the reliability of the run-out accuracy/NRRO, the noise, and theacoustic life, etc., of the spindle motor 1 can be enhanced.

Further, because the base 2 can be configured without the inner wallwhich has conventionally been regarded as necessary for fitting theouter ring 5 of the compound ball bearing 4 to the base 2, the adhesiongroove and the run-off groove that are formed conventionally on theinner peripheral surface of the wall become unnecessary, which reducesman-hours and the manufacturing cost.

Further, since the compound ball bearing 4, the rotary shaft 20, and theconnection member 8 are assembled in advance into one unit, fasteningthe rotary shaft 20 to the rotor hub 3 and fastening the smallerdiameter portion 8 b of the connection member 8 to the base 2 achieveassembly of the compound ball bearing 4 between these two counterparts,and thus the mounting of the compound ball bearing 4 becomes extremelyeasy. In other aspects, the second embodiment exhibits the same effectsas those of the bearing assembly of the first embodiment.

Next, a third embodiment of the invention will be described withreference to FIG. 5 and FIG. 6 wherein the parts corresponding to thoseof the fixed shaft type spindle motor in the first embodiment are giventhe same symbols.

As shown in FIG. 5 and FIG. 6, the fixed shaft type spindle motor 1 ofthe third embodiment has the fixed shaft 10 installed upright(vertically upward) on the flange base 2, with shaft 10 fixed within thecentral circular hole 11 on the flange base 2. Also, the fixed shaft 10is sheathed with a sleeve 31 of a fluid bearing 30.

The sleeve 31 of the fluid bearing 30 is a cylindrical member of aslightly thick wall, and has a step in the upper end thereof, where theinner diameter is enlarged. The larger diameter portion 8 a of thestepped connection member 8 is fixed within the internal recess orstepped portion formed in the upper end of the sleeve 31, with thelarger diameter portion 8 a inserted within the stepped portion. Thesmaller diameter portion 8 b of the connection member 8 is fixed withinthe central circular hole 9 of the rotor hub 3.

Therefore, since the rotor hub 3, connection member 8, and the sleeve 31of the fluid bearing 30 are coupled into a single unit, the rotor hub 3is supported for free rotation by the fixed shaft 10 through theconnection member 8 and the fluid bearing 30. And, since the sleeve 31of the fluid bearing 30 is fixed to the rotor hub 3 through theconnection member 8, the inner peripheral wall which has conventionallybeen regarded as necessary to fit the sleeve 31 of the fluid bearing 30to the rotor hub 3, becomes unnecessary, so that the rotor hub 3 is notprovided with such an inner peripheral surface. The rotor hub 3 has aninner peripheral surface facing the outer peripheral surface of thesleeve 31 of the fluid bearing 30 on the circumferential wall 32 of thecentral smaller diameter portion thereof. However, the sleeve 31 is notfixed to this inner peripheral surface of the circumferential wall 32.

A magnetic disk (not shown) is mounted on the mounting surface 12 of therotor hub 3. The other rotating bodies requiring a high run-outaccuracy/NRRO and/or low noise can be mounted thereon.

Lubricating oil is introduced into the gap between the sleeve 31 of thefluid bearing 30 and the fixed shaft 10. The fixed shaft 10 hasherringbone grooves 33 formed on its outer circumferential surfacethereof at two places which are axially separated. As described later,as the rotor hub 3 rotates, the pressure of the lubricating oil in theherringbone grooves 33 rises, whereby the sleeve 31 floats up on thefixed shaft 10. Here, a gaseous lubricant may replace the lubricatingoil.

A cylindrical thrust ring 34 is fixed to an upper end of the fixed shaft10 by press-fitting. The thrust ring 34 is accommodated or seated in anannular space closed on one side by the inner surface of the connectionmember 8. The annular space is formed as step 36 by enlarging the innerdiameter of the upper end of the sleeve 31. When the sleeve 31 rotatesintegrally with the rotor hub 3, the thrust ring 34 rotates in theannular space relative to the sleeve 31.

Although not detailed in the drawing, herringbones similar to theherringbones 33 formed on the outer circumferential surface of the fixedshaft 10 are formed on an edge surface of the thrust ring 34. Sincelubricating oil is supplied into the gap between the edge surface andthe inner surface of the connection member 8 that faces the edgesurface, as the thrust ring 34 rotates relative to the sleeve 31, theherringbones act to raise the pressure of the lubricating oil, whichfloats the connection member 8 up from the thrust ring 34 and the fixedshaft 10. In this manner, the thrust force acting on the connectionmember 8 is received by the fixed shaft 10, finally by the base 2.

Although not detailed in the drawing, herringbones are formed on thelower edge surface of the sleeve 31. And, since the lubricating oil issupplied into the gap between the lower edge surface of the sleeve 31and the inner surface of the base 2 near the central circular hole 11,as the sleeve 31 rotates integrally with the rotor hub 3, theherringbones formed on the lower edge surface of the sleeve 31 act toraise the pressure of the lubricating oil, which floats the sleeve 31 upfrom the base 2. In this manner, the base 2 also receives the thrustforce acting on the sleeve 31.

The above-described thrust bearing structures may both be used, or oneof these may be omitted.

Although not detailed in the drawing, the lubricating oil thatlubricates the radial bearing portion (the facing sliding surfaces ofthe fixed shaft 10 and the sleeve 31) of the fluid bearing 30 and thrustbearing surfaces (the contacting/sliding surfaces of the thrust ring 34and the connection member 8, and the contacting/sliding surfaces of thesleeve 31 and the base 2) and circulates through these lubricated areasin a closed circulating passage, in a single direction, with therotation of the sleeve 31.

The stator 15 is mounted on the outer peripheral surface of the innercylindrical wall 14 of the base 2, and the permanent magnet 16 ismounted on the inner peripheral surface of the outer circumferentialwall 13 of the rotor hub 3 so as to face the outer peripheral surface ofthe stator 15. A feeder 17 for feeding current to the windings of thestator 15 is connected to the flexible printed circuit board 37.

In the third embodiment, the fixed shaft 10, the fluid bearing 30, theconnection member 8, and the thrust ring 34 are integrally assembled inadvance as a unit, as shown in FIG. 6. With the bearing assembly thusproduced, the projecting end of the fixed shaft 10 thereof is fixedwithin the central circular hole 11 of the base 2, and the smallerdiameter portion 8 b of the connection member 8 is fixed within thecentral circular hole 9 of the rotor hub 3, whereby the fixed shaft typespindle motor 1 of the third embodiment is assembled.

In the third embodiment as described above, when the power is suppliedfrom the feeder 17 to the windings of the stator 15, the rotor hub 3with the permanent magnet 16 starts to rotate as one body with theconnection member 8 and the sleeve 31. That is, the rotor hub 3 is borneby the fluid bearing 30 through the connection member 8 for rotationabout the fixed shaft 10.

The third embodiment thus configured exhibits the following effects.

In the fixed shaft type spindle motor 1 of the third embodiment also,the inner peripheral wall, which has conventionally been regarded asnecessary for fitting the sleeve 31 of the fluid bearing 30 on the rotorhub 3 can be omitted from the rotor hub 3. As a result, the stress whichwould otherwise result from the shape precision (circularity,cylindricality, surface roughness) of the inner peripheral surface ofthe wall, and the stress otherwise caused by mounting the bearing areeliminated. Accordingly, adverse influences on the precision of thesliding surfaces of the sleeve 31 and the fixed shaft 10 are eliminatedand the clearance between their sliding surfaces is ensured, i.e., isconstant, so that the reliability of the run-out accuracy/NRRO, thenoise, the acoustic life, and the rigidity, etc., of the spindle motor 1are enhanced.

Further, because the rotor hub 3 can be configured without the innerperipheral wall which has conventionally been regarded as necessary forfitting the sleeve 31 of the fluid bearing 30 to the rotor hub 3 iseliminated, the adhesion groove and the run-off groove that areconventionally formed on the inner peripheral surface of the wall becomeunnecessary, which reduces the man-hours and the manufacturing cost.

Further, since the fluid bearing 30, the fixed shaft 10, the connectionmember 8, and the thrust ring 34 are assembled in advance into one unit,fastening the fixed shaft 10 to the base 2 (being the other one of thetwo counterparts that mount the bearing assembly therebetween) andfixing the smaller diameter portion 8 b of the connection member 8 tothe rotor hub 3 serve to assemble the fluid bearing 30 between these twocounterparts, and thus the mounting work of the fluid bearing 30 becomesextremely easy to perform. Here, the lubricating oil is introduced afterfinishing the assembly.

Next, a fourth embodiment of the invention will be described withreference to FIG. 7 and FIG. 8. The parts corresponding to those of therotary shaft type spindle motor in the second embodiment and those ofthe fixed shaft type spindle motor in the third embodiment are given thesame symbols.

As shown in FIG. 7 and FIG. 8, the rotary shaft type spindle motor 1 ofthe fourth embodiment has the rotary shaft 20 fixed withing the centralcircular hole 9 on the rotor hub 3. Also, the rotary shaft 20 issheathed with the sleeve 31 of the fluid bearing 30.

The sleeve 31 of the fluid bearing 30 is a cylindrical member of aslightly thick wall, and has a step formed in the lower end thereof,which is made by enlarging the inner diameter. The larger diameterportion 8 a of the stepped connection member 8 is fixed withing the stepformed in the lower end of the sleeve 31. The smaller diameter portion 8b of the connection member 8 is fixed withing the central circular hole11 of the base 2.

Therefore, since the base 2, connection member 8, and the sleeve 31 ofthe fluid bearing 30 are coupled into one unit, the base 2 supports therotary shaft 20 of the rotor hub 3 for free rotation through theconnection member 8 and the sleeve 31 of the fluid bearing 30. And,since the sleeve 31 of the fluid bearing 30 is fixed to the base 2through the connection member 8, the inner peripheral wall (refer to theinner peripheral surface of the inner cylindrical wall 014 of the base02 in FIG. 11), which has conventionally been regarded as necessary forfitting the sleeve 31 of the fluid bearing 30 to the base 2, becomesunnecessary and is omitted. The base 2 has the inner cylindrical wall 14formed upright thereon, and the cylindrical wall 14 has an innerperipheral surface facing the outer peripheral surface of the sleeve 31.However, the sleeve 31 is not fixed to this inner peripheral surface ofthe cylindrical wall 14.

The cylindrical thrust ring 34 is fixed on a lower end of the rotaryshaft 20 by press-fitting. The thrust ring 34 is accommodated in anannular space closed on one side by the inner surface of the connectionmember 8 and formed as a step portion 36 by enlarging the inner diameterof the lower end of the sleeve 31. When the rotary shaft 20 rotates, thethrust ring 34 rotates in the annular space integrally with the rotaryshaft 20.

Although not detailed in the drawing, herringbones similar to theherringbones 33 formed on the outer circumferential surface of therotary shaft 20 are formed on the edge surface of the thrust ring 34.And, since the lubricating oil is supplied into a gap between the edgesurface and the inner surface of the connection member 8 that faces theedge surface, as the thrust ring 34 rotates integrally with the rotaryshaft 20, the herringbones raise the pressure of the lubricating oil,which floats the rotary shaft 20 and the thrust ring 34 up from theinner surface of the connection member 8. In this manner, the thrustforce acting on the rotary shaft 20 is received.

Although not detailed in the drawing, the lubricating oil thatlubricates the radial bearing portion (the interface between the rotaryshaft 20 and the sleeve 31) of the fluid bearing 30 and the thrustbearing portion (the interface between the thrust ring 34 and theconnection member 8) circulates between these interfaces through aclosed circulating passage, in a single direction, with the rotation ofthe rotary shaft 20. A through hole 35 forms a part of the passage.

In the fourth embodiment, the rotary shaft 20, the fluid bearing 30, theconnection member 8, and the thrust ring 34 are integrally assembled inadvance as a unit, as shown in FIG. 8. With the bearing unit thusproduced, the projecting end of the rotary shaft 20 thereof is fixedwithing the central circular hole 9 of the rotor hub 3, and the smallerdiameter portion 8 b of the connection member 8 is fixed within thecentral circular hole 11 of the base 2, whereby the rotary shaft typespindle motor 1 of the fourth embodiment is assembled.

The fourth embodiment is different from the third embodiment in terms ofthe foregoing features, however in other respects it is no differentfrom the other, previously described embodiments, and a detaileddescription of such other features will be omitted.

In the fourth embodiment, when the power is supplied from the feeder 17to the windings of the stator 15, the rotor hub 3 with the permanentmagnet 16 starts to rotate as one body with the rotary shaft 20. Thebase 2 supports the rotary shaft 20 of the rotor hub 3 for free rotationthrough the connection member 8 and the fluid bearing 30.

In the fourth embodiment also, because the inner peripheral wall whichhas conventionally been regarded as necessary for fitting the sleeve 31of the fluid bearing 30 to the base 2 is omitted, the stress resultingfrom the shape precision (circularity, cylindricality, surfaceroughness) of the inner peripheral surface of the wall, and the stresscaused by the press-fitting, adhesion, or press-fit adhesion in mountingthe bearing are eliminated, adverse influences on the precision of thesliding surfaces of the sleeve 31 and the rotary shaft 20 are eliminatedand the clearance between these sliding surfaces is ensured to remain ata constant quantity, so that the reliability of the run-outaccuracy/NRRO, the noise, the acoustic life, and the rigidity, etc., ofthe spindle motor 1 are enhanced.

Further, because the base 2 can be configured without the innerperipheral wall which has conventionally been regarded as necessary forfitting the sleeve 31 of the fluid bearing 30 to the base 2 the adhesiongroove and the run-off groove that are conventionally formed on theinner peripheral surface of the wall become unnecessary, which reducesthe man-hours and lowers the manufacturing cost.

Further, since the fluid bearing 30, the rotary shaft 20, the connectionmember 8, and the thrust ring 34 are assembled in advance into a singleunit, fastening the rotary shaft 20 to the rotor hub 3 (to form one ofthe two counterparts) and fixing the smaller diameter portion 8 b of theconnection member 8 to the base 2 (the other counterpart) will serve toassemble the fluid bearing 30 between these two counterparts, and thusthe mounting work of the fluid bearing 30 becomes extremely easy toperform. Here, the lubricating oil is introduced after finishing theassembling.

In the first through fourth embodiments, it is assumed that the bearingassemblies are each incorporated into spindle motors; however, they canalso be applied to various other rotating machines that require a highrun-out accuracy/NRRO and/or low noise.

As many widely different embodiments of the present invention can bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsdescribed above except as defined in the appended claims.

What is claimed is:
 1. A fluid bearing assembly comprising: a sleeve sheathing a shaft; a cylindrical connector having an outer cylindrical surface which is stepped to form a first diameter portion and a second diameter portion having a diameter smaller than said first diameter portion, one of said first and second diameter portions being fixed to said sleeve; and a member having an aperture receiving and fixing the other of said first and second diameter portions, to provide for relative rotation between said member and said shaft.
 2. A fluid bearing assembly according to claim 1 wherein said shaft is fixed and said member, said connector and said sleeve are rotatable, as one integral unit, around said shaft.
 3. A fluid bearing assembly according to claim 1 wherein said cylindrical connector has at least two steps in its outer cylindrical surface forming said first diameter portion, said second diameter portion and a third diameter portion located between said first and second diameter portions, thereby providing axial spacing between said sleeve and said member.
 4. A fluid bearing assembly according to claim 1 wherein one end of said sleeve has a cylindrical recess, said first diameter portion being fitted within said recess.
 5. A fluid bearing assembly according to claim 1 wherein said member is a hub including a planar, circular plate having said aperture centered therein and a skirt integral with the periphery of said plate and extending perpendicular from said plate along a central axis defined by said shaft.
 6. A fluid bearing assembly according to claim 1 wherein said member, said connector and said sleeve are fixed, as one integral unit, and said shaft is rotatably supported by said sleeve.
 7. A fluid bearing assembly according to claim 1 wherein said first diameter portion is fixed to said sleeve.
 8. A fluid bearing assembly according to claim 2 wherein said first diameter portion is fixed to said sleeve.
 9. A fluid bearing assembly according to claim 6 wherein said first diameter portion is fixed to said sleeve. 